This invention relates to machines for packaging individual rolls or groups of rolls in a film. Such machines are described in detail in U.S. Pat. Nos. 5,433,063, 5,228,273, 4,430,844, 5,255,495 and U.S. patent application Ser. Nos. 08/147,153 and 08/143,455 now U.S. Pat. No. 5,462,013.
Such packaging machines are particularly useful for wrapping rolls of bathroom tissue or household paper towels. Such rolls conventionally include a core and paper wound around the core. One or more wound rolls are overwrapped with a tube of plastic film, and the edges of the film are sealed to form a package.
Prior to this invention, the overwrapping process was continuous motion, consisting of multiple lane product infeed choke belt conveyors. The conveyors feed product in time to a flighted chain conveyor in the desired package format across a dead plate to an overhead chain conveyor with attached product pusher paddles. The product continues to be conveyed in time, pushed by the overhead conveyor pusher paddles across another dead plate to a girth former which overwraps the product with continuously unwound film from an unwind positioned at 90xc2x0 to the flow of product through the machine. The film entubes the product is then overlapped and sealed in a longitudinal direction. The wrapped product is advanced downstream via conveyor pull belts, and perforations in the film produced at the unwind section are severed by timed paddles which impinge the sealed tube of film exactly where the circumferential perforations are positioned exactly halfway between the entubed wrapped products. At this point, the longitudinally sealed overwrapped product becomes separated at the film perforations. Film extending beyond the ends of the product remain for sealing the ends of the package downstream later in the process.
The product continues to be transported via conveyor belts and then is transferred by an overhead chain conveyor with pushers attached which are timed to convey product at 30xc2x0 to the direction of flow. Another chain conveyor with pushers attached traveling beneath a dead plate on which the product rests intercepts the product and pushes it a full 90xc2x0 from the initial direction of travel. While the product continues to be conveyed, air blasts, fixed slotted plates, and flex wipe brush conveyors guide and fold the film on the ends of the product in the same manner as if wrapping a gift. Once the film has been folded, the product is conveyed between moving Teflon(copyright) belts which transport the product via the ends of the package. The belts pass over spring loaded fixed heaters to seal the plastic film on the package ends. The belts continue to transport the package through an unheated area while still maintaining the package under compression to permit cooling of the sealed film.
Products can be packaged with cores up or down and in one or two levels of product. A customer perforation can also be added to the package as an option provided in the film unwind section. The machine sections are driven by a plurality of AC servo motors at guaranteed speeds for individually wrapping rolls of household paper towels at up to 250 packages per minute (ppm).
The ends of the package are sealed by top and bottom sealing dies which close on the film between products. U.S. Pat. No. 5,433,063 describes how the sealing dies (and half dies) are positioned on belts (two half dies located 180xc2x0 apart on each belt), how they are driven, the velocity profile of the dies, how power is transmitted to the belts, and the ability for the dies to be rotated about shaft interlinks on the pairs of belts to which they are attached. The sealing dies include four sealing wires and a cutoff knife.
U.S. Pat. No. 5,433,063 also describes multiple axes for independently driving each of the die sets at a variable velocity. The velocity of the axes relative to one another may be changed during a package making cycle without one die set interfering with any other die set. The actual velocity and acceleration of any given die at various positions within that die""s travel is described in the patent.
The relationship of the velocity and acceleration of each die half with respect to the position of that die half within its travel is referred to as the motion profile. The profile described in the patent is based around the velocity of the film. The velocity of the die is equal to the film velocity as the die half makes contact with the film. The die half then slows down to collapse the film between the bundles. As the die continues around the radius of the pulley, it begins to accelerate back to film velocity. The die half (with the bundle in front of it) will travel at film velocity until the next die half (following the current one) touches the film. Then the first die half decelerates to allow the next die half to collapse the film tube. After that die half finishes collapsing the film tube, both will accelerate back to film velocity.
In U.S. Pat. No. 5,433,063, although not described, cam tracks are used in conjunction with cam followers mounted in various locations on the half dies. Together they serve as a means to control the orientation and path of travel of the half dies. The patent goes on to describe in column 3 that speeds of 45 packages per minute are attainable. This capability is based on a combination of the software programming for the velocity profile of the dies, the size of the servo motors/motion controllers, the inertia based on the weight of the dies and driven components, and the cam track geometry.
Like existing prior art, the invention is also a continuous motion apparatus and process. The invention may also incorporate a similar multiple lane product infeed choke belt conveyor and flighted chain conveyor. At this point the process can begin to differ. The ability to converge product in this area from three or four lanes of product rather than converging product upstream with a separate product diverting conveyor can be provided. Product then transfers from the flighted chain conveyor in time to an overhead conveyor with pushers that push product in time across a dead plate to the girth former. The machine can have a standard forming shoulder overhead and drop away dead plate. A girth former which is breathable or fixed overwraps product with continuously unwound film from an unwind positioned under the drop away dead plate in line with the machine. The film is not perforated. However, the film does entube the product and is then overlapped and sealed in a longitudinal direction in a manner similar to existing art. The entubed product continues downstream via conveyor side pull belts on either side of the product along with top and a bottom conveyor belts, again like existing art. Top pull belts can be substituted with fixed product hold down guides.
Unlike the prior art, this process continues in a straight line where product from the pull belt section transfers over a fixed dead plate and gap to the sealing section. The entubed product begins to travel at a slightly reduced speed, causing the pitch between the products to shorten. At this point the film gussets are tucked by timed air blasts simultaneously on each side of the package just before servo driven traveling top and bottom sealing dies close on the film between the packages. An impulse of current simultaneously seals leading and trailing packages on either side of the sealing dies and cuts the film to separate the packages. All of this is accomplished with one sealing/cutting wire. With a simplified die design, higher operating speeds are possible. Higher speeds are also made possible through the use of programming the software for the drive controllers of the servo motors to provide the appropriate velocity profile of the sealing die to achieve a given operating speed.
This process has been designed to package a single roll of household paper toweling or four rolls of bathroom tissue in a cores down application at an operating speed of 160 ppm. The design speed for the process is 200 ppm.
Although the specific embodiment described herein is for cores down and a single level of product, products can also be packaged cores up and in two levels as well. The invention can also accommodate product of varying individual roll density ranging from soft to hard and non-compressible product.
The construction and application of the motion profile of the sealing dies differs from the previous art in several significant ways. The new profile calculations are approached differently to begin with and, in the end, result in cubic motion throughout the entire profile. Cubic motion gradually changes the acceleration to reduce peak jerk levels and ease the burden on the mechanical assemblies.
The new profile consists of two major sections: the sealing move and the return move. The sealing move commences at the point where the die half first touches the film and ends when the die halves are no longer under pressure. At this point, the dies are no longer gripping the package, though they may be pushing it toward the discharge. The return move commences at this point and ends when the die half again touches the film and begins the sealing move for the next package.
In the previous art, the proximity switch was deemed the starting point of the profile. The die half would accelerate or decelerate from there to the point where it touched the film. The new profile calculations begin at the point where the die touches the film. From that point to the end of the sealing distance, all velocities and distances are directly determined by the dimensions of the cam track and package configuration. Once there are calculated, the entire distance from the end of the sealing move to the next die at film point is available for the return move. It is no longer limited in any way by the location of the proximity switch.
The new profile also eliminates several die profile parameters that, in the previous art, were required to configure the profile to different package sizes. For example, the xe2x80x9cdie offset 1xe2x80x9d parameter was used to vary the space between the dies after they closed for differing package configurations. The new profile calculates all the necessary velocities and distances automatically for each configuration. It does this by comparing the master and slave travel distances throughout the sealing move, taking into account such variables as where the die will be placed between the packages, the distance the die must slow down to allow the incoming product to catch up with it, and the distance the lead package must slow down to collapse the film.
A return move is then calculated depending on the time and distance left after the sealing move is complete. A speed up segment may be added if it is determined that the die will impede the package as it exits the discharge.
The new profile is first developed as a quadratic profile with the eventual conversion to cubic motion as a major consideration. The previous art divided all speed up or slow down moves into standard trapezoidal motion where the master distance is evenly divided by three. The new profile calculations attempt to divide the moves evenly in two with the realization that the peak changes of acceleration will be smoothed out with the cubic motion conversion. Sometimes, however, a maximum or minimum velocity will force the addition of a third segment. The die during this segment will travel at this velocity limit for the minimum distance necessary and then resume acceleration. This keeps the acceleration rates at a minimum while remaining within velocity limits.
After this quadratic profile is calculated, it is then converted to the more complex cubic motion profile. Each segment of the quadratic profile that contains a change in velocity is divided in half, and the acceleration is distributed such that it is increasing during the first half and decreasing during the second half. This results in a curved velocity profile that significantly reduces abrupt changes in acceleration which, in turn, reduces mechanical stress on the moving parts and undesirable motion of the half dies as they touch the film and come together at the beginning of sealing.
The path of travel of the dies is controlled by a closed loop linear bearing hardened steel xe2x80x9cVxe2x80x9d track. Each edge of the track has an opposed xe2x80x9cVxe2x80x9d shape. It is comprised of two horizontal sections some distance apart while inline and parallel to each other. They are joined at each end by a full radius section. Its appearance resembles that of an oval xe2x80x9crace trackxe2x80x9d positioned in a vertical plane. Four linear bearing and track systems are used to support and guide the half dies. Two of the linear bearing track systems are used to support and guide the upper half dies, and two support and guide the lower half dies. The tracks for the upper dies are offset to each other three inches horizontally and vertically. The dies are positioned between the tracks to split the difference between the total horizontal and vertical offset. In this way both the upper and lower half dies can maintain a vertical orientation throughout their path of travel. This is further achieved by a reduced center of gravity of the half dies with respect to their respective offset and to the design of the carriages to which the half dies are attached.
The carriages, like the previous art, utilize a rotatable shaft to permit the desired orientation of the half dies in conjunction with the linear bearing track systems. The carriages incorporate a center rotatable shaft opposed on either side by bogie arms. All of these components incorporate tapered roller bearings. The wheels attached to the bogie arms of the carriage have an opposed xe2x80x9cVxe2x80x9d profile which capture and travel on the opposed xe2x80x9cV""sxe2x80x9d of the track. The design of the carriage imparts a particular stiffness which is important in maintaining control of the vertical position of the half dies at speed.
Mechanically, the carriages in conjunction with the geometry of the linear bearing track system make it possible to achieve a design speed of 200 packages per minute and an operating speed of 160 packages per minute. This is further made possible as a result of software programming for the velocity profile of the half dies and reduced component weight as previously mentioned. In addition to promoting higher speeds than the previous art, this invention provides a means for better control of the half dies by not utilizing a path of travel which incorporates vertical motion of the half dies. The only support the half dies have in the previous art when traveling vertically in their path of travel is that given by the belts to which the half dies are attached. The full radius sections of the track in this invention provide more support, stability and therefore control of the half dies while they are in motion.